JP2538902B2 - X-ray exposure mask - Google Patents

Description

Description: [Object of the invention] (Field of industrial application) The present invention relates to an improvement of an X-ray exposure mask, and more particularly to an X-ray exposure mask in which the warp of a mask substrate support is eliminated.

(Prior Art) In recent years, with the high integration of integrated circuits, the importance of a lithographic technique for forming a pattern on a photosensitive agent is increasing among the fine processing techniques of circuit patterns. Currently, photolithography technology using light as an exposure medium is used in mass production lines, but this technology has a resolution limit that is determined by the wavelength used, and as a new lithography technology to replace this, X-wavelength shorter than light is used. Research and development of X-ray exposure technology using X-rays is making rapid progress.

In X-ray exposure, an X-ray exposure mask on which a predetermined pattern is formed and the sample are held in parallel at intervals of the order of 10 μm, and X-rays are radiated from the back surface of the mask so that the mask pattern is exposed on the sample. Is transcribed to. Where X
The line exposure mask is a thin film (mask engine) of X-ray transparent Si, SiN, SiC, BN or the like deposited on a substrate support such as a silicon wafer by a CVD method or the like, and then X-ray is formed on the thin film. A pattern is formed from a heavy metal such as Au that absorbs, and the central portion of the support is removed by etching from the back surface side according to the shape of the mask substrate.

Although there are many problems to be solved for the practical use of X-ray exposure, the demand for the dimensional accuracy of the mask remains the greatest problem. In order to achieve the pattern transfer of 0.5 μm or less, which is the goal of X-ray exposure, pattern alignment on the order of 0.01 μm is required. Exposure use 10
In the soft X-ray region with a wavelength of about Å, in order for the X-ray intensity after passing through the mask substrate to carry the energy in the sensitivity region of the photosensitizer, a substance such as Si, N, C, B having a small atomic weight should be used. Even when used as a mask substrate, the thickness of the substrate must be very thin, 1-2 μm. Therefore, a heavy metal pattern is present on a very thin mask substrate, and the substrate is apt to be distorted so that the mask pattern arrangement is likely to be displaced. Then, this decrease in pattern arrangement accuracy causes a decrease in pattern transfer accuracy.

In order to overcome this problem, the internal stress of the thin film is usually reduced to 10
The tensile stress of the order of ⁹ dyn / cm ² eliminates the slack of the mask substrate and suppresses the influence of the internal stress of the heavy metal pattern on the substrate as much as possible. However, this strong tensile stress causes the substrate support to warp, as shown in FIG. This significantly impairs the flatness of the mask, making it difficult to control the mask-sample gap. Such warpage can be forcibly corrected by chucking when the mask is set on the aligner, but in this case, complicated distortion occurs in the mask itself, which is not very practical. In FIG. 3, reference numeral 21 is a support made of a silicon substrate, and 22 is a thin film (mask substrate) made of SiN.

On the other hand, when focusing on the gap between the mask and the sample, the maximum deviation from the flatness allowed for the mask substrate is the maximum in order to realize a 0.5 μm pattern by performing X-ray exposure under the currently technically possible conditions. It is 1 μm. However, with the above-mentioned tensile stress values, when a 3 ″ φ substrate support is used,
The maximum warp of the support reaches 10 μm. Therefore,
It is important to control this strong tensile stress in some way.

One method is to optimize the conditions for forming a thin film to be a mask substrate, that is, to form a thin film with a small tensile stress by specifying the type and flow rate ratio of the raw material gas, the forming temperature, and the forming method. Is being done. In this case, although the warp of the substrate support can be reduced, the tensile stress of the mask substrate itself is uniformly reduced, so that wrinkles and slack are generated on the substrate when the back surface is etched.

As another method, in order to suppress the warp occurring in the substrate support while leaving the tensile stress on the mask substrate, a second film 23 having a compressive stress property is formed on the support 21 as shown in FIG. It has been reported that the layer is formed into a multi-layer structure, and the warpage of the support is reduced by the offsetting action of opposing stresses (Reference J. Vac.Sic.Technol.B, vol4, No.1.1986 (221)).
However, in order to realize such a multilayer structure, not only a large number of processes are added but also the process of forming a film is generally difficult to control. In addition, there is a report that the stress is reduced by introducing impurities into the entire surface of the thin film, but this not only reduces the stress of the mask substrate as described above, but also the annealing in the mask substrate. There is a risk of defects that cannot be recovered.

(Problems to be solved by the invention) Conventionally, when the tensile stress of the thin film is increased,
No wrinkles or slack is generated on the mask substrate, but the substrate support is warped. On the contrary, if the tensile stress of the thin film is reduced, the warp of the substrate support can be reduced, but wrinkles and slack are generated in the mask substrate. Further, if a multi-layer structure is adopted to solve both of these problems, there is a problem that the manufacturing process becomes complicated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to realize a simple manufacturing process that can reduce the warp of a substrate support while sufficiently leaving the tensile stress of the mask substrate. It is possible to provide an X-ray exposure mask that can contribute to improving the accuracy of X-ray exposure.

[Structure of the Invention] (Means for Solving Problems) The essence of the present invention is to introduce impurities into a region of a thin film formed on a mask substrate support, excluding a portion to be a mask substrate, The internal stress at is smaller than that at the portion which becomes the mask substrate.

That is, according to the present invention, an X-ray transparent thin film is deposited on the surface of a mask substrate support, and the thin film portion obtained by etching the central portion of the support from the back side is used as a mask substrate for X-ray exposure. In the mask, the impurities are selectively introduced into a region of the thin film on the surface side of the support, excluding a portion serving as the mask substrate.

(Function) It is known that the introduction of impurities generally causes a change in the internal stress of the thin film. However, in the present invention, the impurities are selected in the mask substrate frame portion (the region other than the portion of the thin film to be the mask substrate). The internal stress in the region can be reduced or reversed by the selective introduction. Therefore, the stress applied to the mask substrate support can be reduced while leaving a sufficiently large tensile stress in the mask substrate. Therefore, the warp of the substrate support can be reduced without causing wrinkles or slack of the mask substrate.

(Examples) The details of the present invention will be described below with reference to illustrated examples.

1 (a) and 1 (b) show an X according to an embodiment of the present invention.
It is sectional drawing which shows the manufacturing process of the mask for line exposure.

First, as shown in FIG. 1 (a), 3 ″ φ, thickness 400 μ
NH ₃ and SiH ₂ Cl ₂ gas were made to flow at a ratio of 1: 4 by LPCVD equipment on the entire outer surface of the silicon substrate (mask substrate support) 11 of m in thickness of 1 μm at a temperature of 850 ° C. To the thickness of. Then, as shown in FIG. 1 (b), a resist 13 is provided on the central 1 ″ φ portion to be the mask substrate, and Ar ⁺ ions 14 are implanted into the SiN film 12 at an acceleration voltage of 250 KeV. At this time, the resist 13 serves as a mask for ion implantation, and the Ar ⁺ ions 14 are implanted only in a region of the upper surface of the silicon substrate 11 other than the portion of the SiN film 12 serving as the mask substrate.

Then, as shown in FIG. 1C, the SiN film 12 on the back surface side
Is removed by dry etching, and the silicon substrate 11 is wet-etched with a 30% KOH aqueous solution using the SiN film 12 as a mask as shown in FIG.
By this etching, a thin film portion serving as a 1 ″ φ mask substrate is formed in the opening of the silicon substrate 11 to complete the X-ray exposure mask. A heavy metal pattern (not shown) is formed on the mask substrate. Has been done.

Here, in the case where ion implantation was not performed, the warp of the silicon substrate 11 caused by removing the entire SiN film 12 on the back surface side by dry etching in FIG. 1A was 15 μm as shown in FIG. The radius of curvature was calculated from this value, and the stress of the SiN film was calculated based on the following formula. The tensile stress was about 10 ⁹ dyn / cm ² .

Where E: Young's modulus of thin film [dyn / cm ² ] ν: Poisson's ratio of thin film b: Thickness of silicon substrate [cm] R: Radius of curvature of silicon substrate [cm] D: Thickness of thin film [cm] is there. When a 1 ″ φ mask substrate was formed in the center of this wafer, the average warp of the wafer was 12 μm, and the magnitude of distortion in the mask substrate portion was 2 μm on average.

On the other hand, as in this example, when Ar ⁺ ions were implanted at a rate of 1 × 10 ¹⁵ cm ^{2 in} the step shown in FIG. 1 (b), the wafer warpage was 4 on average in the same mask.
μm, and distortion inside the mask substrate could be suppressed to 0.9 μm.

Thus, according to the present embodiment, the SiN film 12 formed on the surface of the silicon substrate 11 is A
By implanting r ⁺ ions, the warp of the Si substrate 11 can be reduced without reducing the tensile stress of the mask substrate. That is, the warp of the substrate support can be reduced without causing wrinkles or slack of the mask substrate. In this case, unlike the method of adopting the multilayer structure, it can be realized by a simple process of only adding an ion implantation process. Furthermore, since impurities are not introduced into the portion that will become the mask substrate, there is no inconvenience such as the occurrence of defects in the mask substrate. Therefore, it becomes possible to manufacture an X-ray exposure mask having good flatness without wrinkling or slack of the mask substrate, and its usefulness is great.

The present invention is not limited to the above embodiment. For example, the type of ions implanted into the thin film is not limited to Ar ⁺ , but Ne ⁺ , O ^{+ and the} like are also possible. further,
Depending on the type of thin film, it is possible to introduce impurities not only by ion implantation but also by diffusion of B or P. Further, the mask for introducing impurities is not limited to the resist,
The obstacle may be a simple obstacle, and the shape of the mask can be arbitrarily selected as long as the impurities are not introduced into the thin film of the mask substrate portion.

Further, as the mask substrate support, it is possible to use a quartz substrate instead of the silicon substrate. Further, as the thin film material, BN, SiC or the like can be used instead of SiN. In addition, within the scope of the present invention,
Various modifications can be implemented.

[Effects of the Invention] As described in detail above, according to the present invention, by selectively introducing impurities into the thin film forming the X-ray exposure mask, the support can be formed while leaving necessary tensile stress in the mask substrate. The flatness of can be kept excellent. Therefore, it is possible to reduce the warp of the substrate support without causing wrinkles and slack of the mask substrate, and it is possible to contribute to the improvement of the exposure accuracy of X-ray exposure.

[Brief description of drawings]

FIG. 1 is a sectional view showing a manufacturing process of an X-ray exposure mask according to an embodiment of the present invention, and FIG. 2 is a schematic view for explaining a warp of a substrate support caused by a tensile stress of a thin film. Three
FIG. 4 and FIG. 4 are respectively for explaining a conventional example, and FIG. 3 is a sectional view showing an X-ray exposure mask in which warpage has occurred,
FIG. 4 is a cross-sectional view showing an X-ray exposure mask having a multilayer structure. 11 …… Silicon substrate (mask substrate support), 12 …… SiN
Membrane (thin film), 13 …… resist, 14 …… Ar ⁺ ion (impurity).

Claims (5)

(57) [Claims] 1. An X-ray transparent thin film is deposited on the surface of a mask substrate support, an opening is formed by etching the central portion of the support from the back surface side, and the thin film is located at this opening. An X-ray exposure mask having a portion as a mask substrate, wherein impurities are selectively introduced into a region of the thin film on the surface side of the support except a portion to be the mask substrate. The X-ray exposure mask according to item 1. 2. The X-ray exposure mask according to claim 1, wherein the introduction of the impurities is performed by ion implantation. 3. The X-ray exposure mask according to claim 1, wherein the introduction of the impurities is performed by diffusion. 4. The thin film is one in which tensile stress acts as internal stress, and the internal stress of the thin film on the support is smaller than the internal stress of the thin film serving as the mask substrate. X according to claim 1.
Line exposure mask. 5. A thin film on which tensile stress acts as an internal stress, and the internal stress of the thin film on the support is a compressive stress.
An X-ray exposure mask according to the item.